Constructing very high throughput long training field sequences

ABSTRACT

Certain aspects of the present disclosure relate to techniques for constructing a long training field (LTF) sequence in a preamble to reduce a peak-to-average power ratio (PAPR) at a transmitter.

CLAIM OF PRIORITY UNDER 35 U.S.C. §119

This Application is a continuation of U.S. patent application Ser. No.12/731,634, entitled “CONSTRUCTING VERY HIGH THROUGHPUT LONG TRAININGFIELD SEQUENCES”, filed Mar. 25, 2010, now allowed as U.S. Pat. No.8,385,443, which claims benefit of Provisional Application Ser. No.61/226,615, entitled “CONSTRUCTING VERY HIGH THROUGHPUT LONG TRAININGFIELD SEQUENCES”, filed Jul. 17, 2009, which are assigned to theassignee hereof and hereby expressly incorporated by reference herein.

BACKGROUND

1. Field

Certain aspects of the present disclosure generally relate to wirelesscommunications and, more particularly, to construction of a longtraining field (LTF) sequence within a preamble.

2. Background

The Institute of Electrical and Electronics Engineers (IEEE) 802.11 WideLocal Area Network (WLAN) standards body established specifications fortransmissions based on the very high throughput (VHT) approach using acarrier frequency of 5 GHz (i.e., the IEEE 802.11ac specification), orusing a carrier frequency of 60 GHz (i.e., the IEEE 802.11adspecification) targeting aggregate throughputs larger than 1 Gigabitsper second. One of the enabling technologies for the VHT 5 GHzspecification is a wider channel bandwidth, which bonds two 40 MHzchannels for 80 MHz bandwidth therefore doubling the physical layer(PHY) data rate with negligible increase in cost compared to the IEEE802.11n standard.

A VHT Long Training Field (LTF) is a part of a transmission preamble,and can be utilized at a receiver side to estimate characteristics ofunderlying multiple-input multiple output (MIMO) wireless channel.Methods are proposed in the present disclosure to construct the VHT-LTFsequence, while providing a low peak-to-average power ratio (PAPR) at atransmitter side.

SUMMARY

Certain aspects of the present disclosure support a method for wirelesscommunications. The method generally includes constructing a longtraining field (LTF) sequence by combining a plurality of interpolatingsequences and one or more other sequences repeated multiple times in aneffort to reduce (or possibly minimize) a peak-to-average power ratio(PAPR) during a transmission of the constructed LTF sequence, andtransmitting the constructed LTF sequence over a wireless channel byutilizing a bandwidth of a first size.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes a constructingcircuit configured to construct a long training field (LTF) sequence bycombining a plurality of interpolating sequences and one or more othersequences repeated multiple times in an effort to reduce (or possiblyminimize) a peak-to-average power ratio (PAPR) during a transmission ofthe constructed LTF sequence, and a transmitter configured to transmitthe constructed LTF sequence over a wireless channel by utilizing abandwidth of a first size.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes means forconstructing a long training field (LTF) sequence by combining aplurality of interpolating sequences and one or more other sequencesrepeated multiple times in an effort to reduce (or possibly minimize) apeak-to-average power ratio (PAPR) during a transmission of theconstructed LTF sequence, and means for transmitting the constructed LTFsequence over a wireless channel by utilizing a bandwidth of a firstsize.

Certain aspects of the present disclosure provide a computer-programproduct for wireless communications. The computer-program productincludes a computer-readable medium comprising instructions executableto construct a long training field (LTF) sequence by combining aplurality of interpolating sequences and one or more other sequencesrepeated multiple times in an effort to reduce (or possibly minimize) apeak-to-average power ratio (PAPR) during a transmission of theconstructed LTF sequence, and transmit the constructed LTF sequence overa wireless channel by utilizing a bandwidth of a first size.

Certain aspects of the present disclosure provide a wireless node. Thewireless node generally includes at least one antenna, a constructingcircuit configured to construct a long training field (LTF) sequence bycombining a plurality of interpolating sequences and one or more othersequences repeated multiple times in an effort to reduce (or possiblyminimize) a peak-to-average power ratio (PAPR) during a transmission ofthe constructed LTF sequence, and a transmitter configured to transmitvia the at least one antenna the constructed LTF sequence over awireless channel by utilizing a bandwidth of a first size.

Certain aspects of the present disclosure support a method for wirelesscommunications. The method generally includes constructing a longtraining field (LTF) sequence by combining a plurality of interpolatingsequences with LTF symbol values associated with at least one of theIEEE 802.11n standard or the IEEE 802.11a standard, wherein the LTFsymbol values cover at least a portion of bandwidth of a first size, andeach of the LTF symbol values is repeated one or more times fordifferent subcarriers, rotating phases of symbols of the LTF sequenceper bandwidth of the first size in an effort to reduce (or possiblyminimize) a peak-to-average power ratio (PAPR) during a transmission ofthe LTF sequence, and transmitting the LTF sequence over a wirelesschannel by utilizing a bandwidth of a second size.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes a firstcircuit configured to construct a long training field (LTF) sequence bycombining a plurality of interpolating sequences with LTF symbol valuesassociated with at least one of the IEEE 802.11n standard or the IEEE802.11a standard, wherein the LTF symbol values cover at least a portionof bandwidth of a first size, and each of the LTF symbol values isrepeated one or more times for different subcarriers, a second circuitconfigured to rotate phases of symbols of the LTF sequence per bandwidthof the first size in an effort to reduce (or possibly minimize) apeak-to-average power ratio (PAPR) during a transmission of the LTFsequence, and a transmitter configured to transmit the LTF sequence overa wireless channel by utilizing a bandwidth of a second size.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes means forconstructing a long training field (LTF) sequence by combining aplurality of interpolating sequences with LTF symbol values associatedwith at least one of the IEEE 802.11n standard or the IEEE 802.11astandard, wherein the LTF symbol values cover at least a portion ofbandwidth of a first size, and each of the LTF symbol values is repeatedone or more times for different subcarriers, means for rotating phasesof symbols of the LTF sequence per bandwidth of the first size in aneffort to reduce (or possibly minimize) a peak-to-average power ratio(PAPR) during a transmission of the LTF sequence, and means fortransmitting the LTF sequence over a wireless channel by utilizing abandwidth of a second size.

Certain aspects of the present disclosure provide a computer-programproduct for wireless communications. The computer-program productincludes a computer-readable medium comprising instructions executableto construct a long training field (LTF) sequence by combining aplurality of interpolating sequences with LTF symbol values associatedwith at least one of the IEEE 802.11n standard or the IEEE 802.11astandard, wherein the LTF symbol values cover at least a portion ofbandwidth of a first size, and each of the LTF symbol values is repeatedone or more times for different subcarriers, rotate phases of symbols ofthe LTF sequence per bandwidth of the first size in an effort to reduce(or possibly minimize) a peak-to-average power ratio (PAPR) during atransmission of the LTF sequence, and transmit the LTF sequence over awireless channel by utilizing a bandwidth of a second size.

Certain aspects of the present disclosure provide a wireless node. Thewireless node generally includes at least one antenna, a first circuitconfigured to construct a long training field (LTF) sequence bycombining a plurality of interpolating sequences with LTF symbol valuesassociated with at least one of the IEEE 802.11n standard or the IEEE802.11a standard, wherein the LTF symbol values cover at least a portionof bandwidth of a first size, and each of the LTF symbol values isrepeated one or more times for different subcarriers, a second circuitconfigured to rotate phases of symbols of the LTF sequence per bandwidthof the first size in an effort to reduce (or possibly minimize) apeak-to-average power ratio (PAPR) during a transmission of the LTFsequence, and a transmitter configured to transmit via the at least oneantenna the LTF sequence over a wireless channel by utilizing abandwidth of a second size.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentdisclosure can be understood in detail, a more particular description,briefly summarized above, may be had by reference to aspects, some ofwhich are illustrated in the appended drawings. It is to be noted,however, that the appended drawings illustrate only certain typicalaspects of this disclosure and are therefore not to be consideredlimiting of its scope, for the description may admit to other equallyeffective aspects.

FIG. 1 illustrates a diagram of a wireless communications network inaccordance with certain aspects of the present disclosure.

FIG. 2 illustrates a block diagram of an example of signal processingfunctions of a physical layer (PHY) of a wireless node in the wirelesscommunications network of FIG. 1 in accordance with certain aspects ofthe present disclosure.

FIG. 3 illustrates a block diagram of an exemplary hardwareconfiguration for a processing system in a wireless node in the wirelesscommunications network of FIG. 1 in accordance with certain aspects ofthe present disclosure.

FIG. 4 illustrates example operations for constructing a very highthroughput long training field (VHT-LTF) sequence for 80 MHz channel inaccordance with certain aspects of the present disclosure.

FIG. 4A illustrates example components capable of performing theoperations illustrated in FIG. 4.

FIG. 5 illustrates example of peak-to-average power ratio (PAPR) resultsfor 80 MHz LTFs designed according to a legacy-based approach inaccordance with certain aspects of the present disclosure.

FIG. 6 illustrates another example of PAPR results for 80 MHz LTFsdesigned according to the legacy-based approach in accordance withcertain aspects of the present disclosure.

FIGS. 7A-7B illustrate example of PAPR results for 80 MHz LTFs designedbased on a first new sequence in accordance with certain aspects of thepresent disclosure.

FIG. 8 illustrates preferred 80 MHz LTFs designed based on the first newsequence in accordance with certain aspects of the present disclosure.

FIGS. 9A-9B illustrate example of PAPR results for 80 MHz LTFs designedbased on a second new sequence in accordance with certain aspects of thepresent disclosure.

FIG. 10 illustrates preferred 80 MHz LTFs designed based on the secondnew sequence in accordance with certain aspects of the presentdisclosure.

FIGS. 11A-11B illustrate example of PAPR results for 80 MHz LTFsdesigned based on a third new sequence in accordance with certainaspects of the present disclosure.

FIG. 12 illustrates preferred 80 MHz LTFs designed based on the thirdnew sequence in accordance with certain aspects of the presentdisclosure.

FIG. 13 illustrates other example operations for constructing a veryhigh throughput long training field (VHT-LTF) sequence for 80 MHzchannel in accordance with certain aspects of the present disclosure.

FIG. 13A illustrates example components capable of performing theoperations illustrated in FIG. 13.

DETAILED DESCRIPTION

Various aspects of the disclosure are described more fully hereinafterwith reference to the accompanying drawings. This disclosure may,however, be embodied in many different forms and should not be construedas limited to any specific structure or function presented throughoutthis disclosure. Rather, these aspects are provided so that thisdisclosure will be thorough and complete, and will fully convey thescope of the disclosure to those skilled in the art. Based on theteachings herein, one skilled in the art should appreciate that thescope of the disclosure is intended to cover any aspect of thedisclosure disclosed herein, whether implemented independently of orcombined with any other aspect of the disclosure. For example, anapparatus may be implemented or a method may be practiced using anynumber of the aspects set forth herein. In addition, the scope of thedisclosure is intended to cover such an apparatus or method which ispracticed using other structure, functionality, or structure andfunctionality in addition to or other than the various aspects of thedisclosure set forth herein. It should be understood that any aspect ofthe disclosure disclosed herein may be embodied by one or more elementsof a claim.

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any aspect described herein as “exemplary”is not necessarily to be construed as preferred or advantageous overother aspects.

Although particular aspects are described herein, many variations andpermutations of these aspects fall within the scope of the disclosure.Although some benefits and advantages of the preferred aspects arementioned, the scope of the disclosure is not intended to be limited toparticular benefits, uses or objectives. Rather, aspects of thedisclosure are intended to be broadly applicable to different wirelesstechnologies, system configurations, networks and transmissionprotocols, some of which are illustrated by way of example in thefigures and in the following description of the preferred aspects. Thedetailed description and drawings are merely illustrative of thedisclosure rather than limiting, the scope of the disclosure beingdefined by the appended claims and equivalents thereof.

An Example Wireless Communication System

The techniques described herein may be used for various broadbandwireless communication systems, including communication systems that arebased on an orthogonal multiplexing scheme. Examples of suchcommunication systems include Orthogonal Frequency Division MultipleAccess (OFDMA) systems, Single-Carrier Frequency Division MultipleAccess (SC-FDMA) systems, and so forth. An OFDMA system utilizesorthogonal frequency division multiplexing (OFDM), which is a modulationtechnique that partitions the overall system bandwidth into multipleorthogonal sub-carriers. These sub-carriers may also be called tones,bins, etc. With OFDM, each sub-carrier may be independently modulatedwith data. An SC-FDMA system may utilize interleaved FDMA (IFDMA) totransmit on sub-carriers that are distributed across the systembandwidth, localized FDMA (LFDMA) to transmit on a block of adjacentsub-carriers, or enhanced FDMA (EFDMA) to transmit on multiple blocks ofadjacent sub-carriers. In general, modulation symbols are sent in thefrequency domain with OFDM and in the time domain with SC-FDMA.

The teachings herein may be incorporated into (e.g., implemented withinor performed by) a variety of wired or wireless apparatuses (e.g.,nodes). In some aspects, a node implemented in accordance with theteachings herein may comprise an access point or an access terminal.

An access point (“AP”) may comprise, be implemented as, or known asNodeB, Radio Network Controller (“RNC”), eNodeB, Base Station Controller(“BSC”), Base Transceiver Station (“BTS”), Base Station (“BS”),Transceiver Function (“TF”), Radio Router, Radio Transceiver, BasicService Set (“BSS”), Extended Service Set (“ESS”), Radio Base Station(“RBS”), or some other terminology.

An access terminal (“AT”) may comprise, be implemented as, or known asan access terminal, a subscriber station, a subscriber unit, a mobilestation, a remote station, a remote terminal, a user terminal, a useragent, a user device, user equipment, or some other terminology. In someimplementations an access terminal may comprise a cellular telephone, acordless telephone, a Session Initiation Protocol (“SIP”) phone, awireless local loop (“WLL”) station, a personal digital assistant(“PDA”), a handheld device having wireless connection capability, orsome other suitable processing device connected to a wireless modem.Accordingly, one or more aspects taught herein may be incorporated intoa phone (e.g., a cellular phone or smart phone), a computer (e.g., alaptop), a portable communication device, a portable computing device(e.g., a personal data assistant), an entertainment device (e.g., amusic or video device, or a satellite radio), a global positioningsystem device, a headset, a sensor or any other suitable device that isconfigured to communicate via a wireless or wired medium. In someaspects the node is a wireless node. Such wireless node may provide, forexample, connectivity for or to a network (e.g., a wide area networksuch as the Internet or a cellular network) via a wired or wirelesscommunication link.

Several aspects of a wireless network will now be presented withreference to FIG. 1. The wireless network 100 is shown with severalwireless nodes, generally designated as nodes 110 and 120. Each wirelessnode is capable of receiving and/or transmitting. In the discussion thatfollows the term “receiving node” may be used to refer to a node that isreceiving and the term “transmitting node” may be used to refer to anode that is transmitting. Such a reference does not imply that the nodeis incapable of performing both transmit and receive operations.

In the detailed description that follows, the term “access point” isused to designate a transmitting node and the term “access terminal” isused to designate a receiving node for downlink communications, whereasthe term “access point” is used to designate a receiving node and theterm “access terminal” is used to designate a transmitting node foruplink communications. However, those skilled in the art will readilyunderstand that other terminology or nomenclature may be used for anaccess point and/or access terminal. By way of example, an access pointmay be referred to as a base station, a base transceiver station, astation, a terminal, a node, an access terminal acting as an accesspoint, or some other suitable terminology. An access terminal may bereferred to as a user terminal, a mobile station, a subscriber station,a station, a wireless device, a terminal, a node or some other suitableterminology. The various concepts described throughout this disclosureare intended to apply to all suitable wireless nodes regardless of theirspecific nomenclature.

The wireless network 100 may support any number of access pointsdistributed throughout a geographic region to provide coverage foraccess terminals 120. A system controller 130 may be used to providecoordination and control of the access points, as well as access toother networks (e.g., Internet) for the access terminals 120. Forsimplicity, one access point 110 is shown. An access point is generallya fixed terminal that provides backhaul services to access terminals inthe geographic region of coverage; however, the access point may bemobile in some applications. An access terminal, which may be fixed ormobile, utilizes the backhaul services of an access point or engages inpeer-to-peer communications with other access terminals. Examples ofaccess terminals include a telephone (e.g., cellular telephone), alaptop computer, a desktop computer, a Personal Digital Assistant (PDA),a digital audio player (e.g., MP3 player), a camera, a game console orany other suitable wireless node.

One or more access terminals 120 may be equipped with multiple antennasto enable certain functionality. With this configuration, multipleantennas at the access point 110 may be used to communicate with amultiple antenna access terminal to improve data throughput withoutadditional bandwidth or transmit power. This may be achieved bysplitting a high data rate signal at the transmitter into multiple lowerrate data streams with different spatial signatures, thus enabling thereceiver to separate these streams into multiple channels and properlycombine the streams to recover the high rate data signal.

While portions of the following disclosure will describe accessterminals that also support multiple-input multiple-output (MIMO)technology, the access point 110 may also be configured to supportaccess terminals that do not support MIMO technology. This approach mayallow older versions of access terminals (i.e., “legacy” terminals) toremain deployed in a wireless network, extending their useful lifetime,while allowing newer MIMO access terminals to be introduced asappropriate.

In the detailed description that follows, various aspects of theinvention will be described with reference to a MIMO system supportingany suitable wireless technology, such as Orthogonal Frequency DivisionMultiplexing (OFDM). OFDM is a technique that distributes data over anumber of subcarriers spaced apart at precise frequencies. The spacingprovides “orthogonality” that enables a receiver to recover the datafrom the subcarriers. An OFDM system may implement IEEE 802.11, or someother air interface standard. Other suitable wireless technologiesinclude, by way of example, Code Division Multiple Access (CDMA), TimeDivision Multiple Access (TDMA), or any other suitable wirelesstechnology, or any combination of suitable wireless technologies. A CDMAsystem may implement with IS-2000, IS-95, IS-856, Wideband-CDMA (WCDMA)or some other suitable air interface standard. A TDMA system mayimplement Global System for Mobile Communications (GSM) or some othersuitable air interface standard. As those skilled in the art willreadily appreciate, the various aspects of this invention are notlimited to any particular wireless technology and/or air interfacestandard.

FIG. 2 illustrates a conceptual block diagram illustrating an example ofthe signal processing functions of the Physical (PHY) layer. In atransmit mode, a TX data processor 202 may be used to receive data fromthe Media Access Control (MAC) layer and encode (e.g., Turbo code) thedata to facilitate forward error correction (FEC) at the receiving node.The encoding process results in a sequence of code symbols that that maybe blocked together and mapped to a signal constellation by the TX dataprocessor 202 to produce a sequence of modulation symbols.

In wireless nodes implementing OFDM, the modulation symbols from the TXdata processor 202 may be provided to an OFDM modulator 204. The OFDMmodulator splits the modulation symbols into parallel streams. Eachstream is then mapped to an OFDM subcarrier and then combined togetherusing an Inverse Fast Fourier Transform (IFFT) to produce a time domainOFDM stream.

A TX spatial processor 206 performs spatial processing on the OFDMstream. This may be accomplished by spatially precoding each OFDM andthen providing each spatially precoded stream to a different antenna 208via a transceiver 206. Each transmitter 206 modulates an RF carrier witha respective precoded stream for transmission over the wireless channel.

In a receive mode, each transceiver 206 receives a signal through itsrespective antenna 208. Each transceiver 206 may be used to recover theinformation modulated onto an RF carrier and provide the information toa RX spatial processor 210.

The RX spatial processor 210 performs spatial processing on theinformation to recover any spatial streams destined for the wirelessnode 200. The spatial processing may be performed in accordance withChannel Correlation Matrix Inversion (CCMI), Minimum Mean Square Error(MMSE), Soft Interference Cancellation (SIC) or some other suitabletechnique. If multiple spatial streams are destined for the wirelessnode 200, they may be combined by the RX spatial processor 210.

In wireless nodes implementing OFDM, the stream (or combined stream)from the RX spatial processor 210 is provided to an OFDM demodulator212. The OFDM demodulator 212 converts the stream (or combined stream)from time-domain to the frequency domain using a Fast Fourier Transform(FFT). The frequency domain signal comprises a separate stream for eachsubcarrier of the OFDM signal. The OFDM demodulator 212 recovers thedata (i.e., modulation symbols) carried on each subcarrier andmultiplexes the data into a stream of modulation symbols.

A RX data processor 214 may be used to translate the modulation symbolsback to the correct point in the signal constellation. Because of noiseand other disturbances in the wireless channel, the modulation symbolsmay not correspond to an exact location of a point in the originalsignal constellation. The RX data processor 214 detects which modulationsymbol was most likely transmitted by finding the smallest distancebetween the received point and the location of a valid symbol in thesignal constellation. These soft decisions may be used, in the case ofTurbo codes, for example, to compute a Log-Likelihood Ratio (LLR) of thecode symbols associated with the given modulation symbols. The RX dataprocessor 214 then uses the sequence of code symbol LLRs in order todecode the data that was originally transmitted before providing thedata to the MAC layer.

FIG. 3 illustrates a conceptual diagram illustrating an example of ahardware configuration for a processing system in a wireless node. Inthis example, the processing system 300 may be implemented with a busarchitecture represented generally by bus 302. The bus 302 may includeany number of interconnecting buses and bridges depending on thespecific application of the processing system 300 and the overall designconstraints. The bus links together various circuits including aprocessor 304, machine-readable media 306 and a bus interface 308. Thebus interface 308 may be used to connect a network adapter 310, amongother things, to the processing system 300 via the bus 302. The networkadapter 310 may be used to implement the signal processing functions ofthe PHY layer. In the case of an access terminal 110 (see FIG. 1), auser interface 312 (e.g., keypad, display, mouse, joystick, etc.) mayalso be connected to the bus. The bus 302 may also link various othercircuits such as timing sources, peripherals, voltage regulators, powermanagement circuits, and the like, which are well known in the art, andtherefore, will not be described any further.

The processor 304 is responsible for managing the bus and generalprocessing, including the execution of software stored on themachine-readable media 306. The processor 304 may be implemented withone or more general-purpose and/or special-purpose processors. Examplesinclude microprocessors, microcontrollers, DSP processors and othercircuitry that can execute software. Software shall be construed broadlyto mean instructions, data or any combination thereof, whether referredto as software, firmware, middleware, microcode, hardware descriptionlanguage, or otherwise. Machine-readable media may include, by way ofexample, RAM (Random Access Memory), flash memory, ROM (Read OnlyMemory), PROM (Programmable Read-Only Memory), EPROM (ErasableProgrammable Read-Only Memory), EEPROM (Electrically ErasableProgrammable Read-Only Memory), registers, magnetic disks, opticaldisks, hard drives, or any other suitable storage medium, or anycombination thereof. The machine-readable media may be embodied in acomputer-program product. The computer-program product may comprisepackaging materials.

In the hardware implementation illustrated in FIG. 3, themachine-readable media 306 is shown as part of the processing system 300separate from the processor 304. However, as those skilled in the artwill readily appreciate, the machine-readable media 306, or any portionthereof, may be external to the processing system 300. By way ofexample, the machine-readable media 306 may include a transmission line,a carrier wave modulated by data, and/or a computer product separatefrom the wireless node, all which may be accessed by the processor 304through the bus interface 308. Alternatively, or in addition to, themachine readable media 306, or any portion thereof, may be integratedinto the processor 304, such as the case may be with cache and/orgeneral register files.

The processing system 300 may be configured as a general-purposeprocessing system with one or more microprocessors providing theprocessor functionality and external memory providing at least a portionof the machine-readable media 306, all linked together with othersupporting circuitry through an external bus architecture.Alternatively, the processing system 300 may be implemented with an ASIC(Application Specific Integrated Circuit) with the processor 304, thebus interface 308, the user interface 312 in the case of an accessterminal), supporting circuitry (not shown), and at least a portion ofthe machine-readable media 306 integrated into a single chip, or withone or more FPGAs (Field Programmable Gate Array), PLDs (ProgrammableLogic Device), controllers, state machines, gated logic, discretehardware components, or any other suitable circuitry, or any combinationof circuits that can perform the various functionality describedthroughout this disclosure. Those skilled in the art will recognize howbest to implement the described functionality for the processing system300 depending on the particular application and the overall designconstraints imposed on the overall system.

The wireless network 100 from FIG. 1 may represent the IEEE 802.11 WideLocal Area Network (WLAN) utilizing the very high throughput (VHT)protocol for signal transmissions with a carrier frequency of 5 GHz(i.e., the IEEE 802.11ac specification) or with a carrier frequency of60 GHz (i.e., the IEEE 802.11ad specification) targeting aggregatethroughputs larger than 1 Gigabits per second. The VHT 5 GHzspecification may utilize a wider channel bandwidth, which may comprisetwo 40 MHz channels to achieve 80 MHz bandwidth therefore doubling thePHY data rate with negligible increase in cost compared to the IEEE802.11n standard.

Certain aspects of the present disclosure support constructing atraining sequence within a preamble for the VHT-based transmissions thatmay provide a lower peak-to-average power ratio (PAPR) than the trainingsequences utilized in the art.

Constructing Long Training Field Sequence for 80 MHz Bandwidth

A Very High Throughput Long Training Field (VHT-LTF) sequence of atransmission preamble may be utilized at a receiver side to estimatecharacteristics of a wireless channel. The 80 MHz VHT-LTF sequence maybe derived based on two approaches. In one aspect of the presentdisclosure, the VHT-LTF may be derived by using two 40 MHz HT-LTFs toretain its low PAPR and high autocorrelation properties. To achievethis, the 40 MHz HT-LTF may be duplicated, shifted in frequency, andthen extra/missing subcarriers may be filled. This approach can bereferred as the “Legacy Approach” since the existing 40 MHz HT-LTFsequences may be utilized. In another aspect of the present disclosure,an entirely new LTF sequence may be constructed in order to obtain evenbetter PAPR results. This approach can be referred as the “New Sequence”approach.

FIG. 4 illustrates example operations 400 for constructing the VHT-LTFsequence for 80 MHz channel bandwidth in accordance with certain aspectsof the present disclosure. At 402, the LTF sequence may be constructedby combining a plurality of interpolating sequences and one or moreother sequences repeated multiple times with appropriately chosen phaserotation (e.g., as defined in FIGS. 7-12 with different rotationalpatterns [c1 c2 c3 c4]) in an effort to minimize (or at least reduce)the PAPR during transmission of the constructed LTF sequence. At 404,the constructed LTF sequence may be transmitted over a wireless channelby utilizing, for example, a bandwidth of 80 MHz.

FIG. 13 illustrates example operations 1300 for constructing the VHT-LTFsequence for 80 MHz channel bandwidth in accordance with certain aspectsof the present disclosure. At 1302, the LTF sequence may be constructedby combining a plurality of interpolating sequences with LTF symbolvalues associated with at least one of the IEEE 802.11n standard or theIEEE 802.11a standard, wherein the LTF symbol values may cover at leasta portion of bandwidth of a first size, and each of the LTF symbolvalues may be repeated one or more times for different subcarriers. At1304, phases of symbols of the LTF sequence may be rotated per bandwidthof the first size (e.g., as defined in FIGS. 7-12 with different valuesof c1, c2, c3 and c4 of rotational patterns applied per 20 MHz sub-band)in an effort to minimize (or at least reduce) the PAPR during atransmission of the LTF sequence. At 1306, the LTF sequence may betransmitted over a wireless channel by utilizing a bandwidth of a secondsize.

Constructing 80 MHz LTF Sequence Based on Legacy Approach

In one aspect of the present disclosure, the 80 MHz LTF sequence may beconstructed by using two 40 MHz 802.11n LTFs as given by:

$\begin{matrix}{{VHTLTF}_{{- 122},122} = {\left\{ {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1,{- 1},{- 1},{- 1},1,{{interp}\; 40\;{Null}},{- 1},1,1,{- 1},1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1,{{interp}\; 80\;{ExtraL}},0,0,0,0,0,{{interp}\; 80\;{ExtraR}},\; 1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1,{- 1},{- 1},{- 1},1,{{inter}\; 40\;{Null}},{- 1},1,1,{- 1},1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1} \right\}.}} & (1)\end{matrix}$

It can be observed from equation (1) that there may exist five zerosubcarriers around the DC tone. Vectors interp40Null, interp80ExtraL,and interp80ExtraR may represent interpolating sequences utilized tofill missing subcarrier values in LTFs for achieving a desiredbandwidth, such as the bandwidth of 80 MHz. Each interpolating sequencemay comprise three subcarriers in this particular case, and may beoptimized in an effort to minimize (or at least reduce) the PAPR.

FIG. 5 illustrates PAPR results for 80 MHz LTFs designed based on theapproach given by equation (1) in accordance with certain aspects of thepresent disclosure. Those cases from FIG. 5 labeled as “with rotation”refer to LTFs generated from equation (1) where the upper frequency bandof 40 MHz may be rotated by 90 degrees. Approaches that utilize256-point inverse Fourier transform (IFFT) with no oversampling beforetransmission (i.e., transmission rate of 80 Mega samples per second) mayprovide lower bounds of PAPRs for oversampling cases, and these PAPRresults may correspond to preferred LTF sequences for cases with andwithout 90 degree phase rotation.

In the case of oversampling with the 1024-point IFFT, the PAPR resultsfor approaches with and without phase rotation may be very close, bothlarger than 7 dB, as illustrated in FIG. 5. These two approaches mayhave different preferred LTF sequences. In the case of 256-point IFFTand oversampling with 4-times time domain interpolation (4× TDI), thePAPR results may largely depend on filtering parameters. For example,listed results in FIG. 5 may be obtained with a filter cutoff frequencyof 0.25, which may be the preferred frequency for this type offiltering. The generated LTF sequence with the 90 degree phase rotationof the upper 40 MHz frequency band may provide the PAPR of 5.8816 dB,which is substantially smaller than the PAPR of 8.7891 dB obtainedwithout the phase rotation.

The subcarrier tones may be further divided into more than two segments,and different phase rotation may be applied on each segment. This mayresult in even lower level of PAPR as the high PAPR may be mainly due totoo many independent subcarriers added together.

If the phase rotation of the upper 40 MHz band is applied as well as theoversampling based on the TDI, then the preferred 80 MHz LTF sequencefor the case defined by equation (1) is with PAPR of 5.8816 dB. Thispreferred LTF sequence may be given as:

$\begin{matrix}{{VHTLTF}_{{- 122},122} = {\left\{ {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1,{- 1},{- 1},{- 1},1,1,{- 1},{{- 1} - 1},1,1,{- 1},1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1,1,{- 1},1,0,0,0,0,0,{- 1},1,{- 1},1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1,{- 1},{- 1},{- 1},1,1,{- 1},{- 1},{- 1},1,1,{- 1},1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1} \right\}.}} & (2)\end{matrix}$It can be observed by comparing equation (2) and equation (1) that theinterpolating sequences may be given as:[interp40Null, interp80ExtraL, interp80ExtraR]=[1 −1 −1, 1 −1 1, −1 1−1]  (3)

In another aspect of the present disclosure, the 80 MHz LTF sequence maybe constructed by using two 40 MHz 802.11n LTFs as given by:

$\begin{matrix}{{VHTLTF}_{{- 122},122} = {\left\{ {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1,{- 1},{- 1},{- 1},1,{{interp}\; 40\;{Null}},{- 1},1,1,{- 1},1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1,{{interp}\; 80\;{ExtraL}},0,0,0,{{interp}\; 80\;{ExtraR}},\; 1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,1,1,1,1,{- 1},{- 1},{- 1},1,{{inter}\; 40\;{Null}},{- 1},1,1,{- 1},1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1} \right\}.}} & (4)\end{matrix}$

It can be observed from equation (4) that there may exist three zerosubcarriers around the DC tone. The interpolating sequencesinterp40Null, interp80ExtraL, and interp80ExtraR may comprise extratones to be chosen in an effort to minimize (or at least reduce) thePAPR.

FIG. 6 illustrates PAPR results for the 80 MHz LTFs designed based onthe approach given by equation (4) in accordance with certain aspects ofthe present disclosure. Those cases from FIG. 6 labeled as “withrotation” refer to LTFs generated from equation (4) where phases oftones of the upper frequency band of 40 MHz may be rotated by 90degrees.

In the case of 256-point IFFT with oversampling based on 4-times timedomain interpolation (4× TDI), the PAPR results may again largely dependon filtering parameters. For example, the PAPR results from FIG. 6 maybe obtained with the filter cutoff frequency of 0.25. The phase rotationof tones from the upper frequency band by 90 degrees may provide thePAPR of 6.0423 dB, as illustrated in FIG. 6, which is substantiallysmaller than the PAPR of 8.5841 dB obtained without phase rotation. Thismay represent the preferred result in the case of oversampling. It canbe observed from FIGS. 5-6 that phase rotation in the upper band maysubstantially reduce the level of PAPR.

If the phase rotation of the upper 40 MHz band is applied as well as theoversampling based on the TDI, then the preferred 80 MHz LTF sequencefor the case defined by equation (4) may provide the PAPR of 6.0423 dB(see FIG. 6). This preferred LTF sequence may be given as:

$\begin{matrix}{{VHTLTF}_{{- 122},122} = {\left\{ {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1,{- 1},{- 1},{- 1},1,1,{- 1},{{- 1} - 1},1,1,{- 1},1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1,{- 1},{- 1},{- 1},{- 1},0,0,0,1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1,{- 1},{- 1},{- 1},1,1,{- 1},{- 1},{- 1},1,1,{- 1},1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1} \right\}.}} & (5)\end{matrix}$It can be observed by comparing equations (4) and (5) that theinterpolating sequences from equation (4) may be given as:[interp40Null, interp80ExtraL, interp80ExtraR]=[1 −1 −1, −1 −1 −1 −1, 11 1 1].  (6)

Constructing 80 MHZ LTF Sequence Based on New Sequence Approach

The 80 MHz LTF sequence may be constructed by using four 802.11a LTFsequences in the 20 MHz subbands covered by a complementary sequence,which may be equivalent to the phase rotation on each subband. Someadditional tone values may be also determined in an effort to minimize(or at least reduce) the PAPR during transmission of the LTF sequence.

In one aspect of the present disclosure, the LTF sequence may beconstructed as:

$\begin{matrix}{{VHTLTF}_{{- 122},122} = {\left\{ {{c\; 1.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,{{interp}\; 20\;{Null}}} \right\rbrack},{c\; 1.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1} \right\rbrack},{{interp}\; 40\;{Null}},{c\; 2.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,{{interp}\; 20\;{Null}}} \right\rbrack},{c\; 2.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1} \right\rbrack},{{interp}\; 80\;{ExtraL}},0,0,0,0,0,{{interp}\; 80\;{ExtraR}},{c\; 3.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,{{interp}\; 20\;{Null}}} \right\rbrack},{c\; 3*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1} \right\rbrack},{{interp}\; 40\;{Null}},{c\; 4.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,{{interp}\; 20\;{Null}}} \right\rbrack},\;{c\; 4.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1} \right\rbrack}} \right\}.}} & (7)\end{matrix}$

It can be observed from equation (7) that there may be five zerosubcarriers around the DC tone, the interpolating sequencesinterp20Null, interp40Null, interp80ExtraL, interp80ExtraR may compriseextra tones to be chosen in an effort to minimize (or at least reduce)the PAPR, and [c1 c2 c3 c4] may represent the complementary sequence.

FIGS. 7A-7B illustrate an example of PAPR results for 80 MHz LTFsdesigned based on the approach given by equation (7) with various phaserotation patterns on 20 MHz subbands in accordance with certain aspectsof the present disclosure. It can be observed from FIGS. 7A-7B that theconstructed new LTF sequences based on four 20 MHz 802.11a LTFs mayprovide, in general, improved PAPR results compared to the previouslyconstructed LTF sequences based on two 40 MHz 802.11n LTFs (i.e., theLTF sequences generated based on the legacy approach and given byequations (2) and (5)).

It can be also observed from FIGS. 7A-7B that the phase rotation ofupper band does not result into PAPR reduction, and the PAPR results areeven worse. Also, the complementary sequences [1 1 1 −1] and [1 −1 1 1]may provide better PAPR results than the sequences [1 1 −1 1] and [−1 11 1], while the complementary sequence [1 1 1 −1] may provide very closePAPR results to [1 −1 1 1] pattern. By using [1 j 1 −j] complementarysequence combined with 90 degree phase rotation of the upper 40 MHz bandand oversampling based on time domain interpolation, the constructed newLTF sequences based on four 20 MHz 802.11a LTFs may provide the PAPR of5.8913 dB. It can be observed that this PAPR result is comparable withthe PAPR result of 5.8816 dB (see FIG. 5) of the LTF sequence defined byequation (2) which is constructed based on two 40 MHz 802.11n LTFs.

The preferred 80 MHz LTF sequence constructed based on four 20 MHz802.11a LTFs and on a complementary sequence may be given as:

$\begin{matrix}{{VHTLTF}_{{- 122},122} = {\left\{ {{c\; 1.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,{{interp}\; 20\;{Null}}} \right\rbrack},{c\; 1.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1} \right\rbrack},{{interp}\; 40\;{Null}},{c\; 2.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,{{interp}\; 20\;{Null}}} \right\rbrack},{c\; 2.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1} \right\rbrack},{{interp}\; 80\;{ExtraL}},0,0,0,0,0,{{interp}\; 80\;{ExtraR}},{c\; 3.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,{{interp}\; 20\;{Null}}} \right\rbrack},{c\; 3*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1} \right\rbrack},{{interp}\; 40\;{Null}},{c\; 4.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,{{interp}\; 20\;{Null}}} \right\rbrack},\;{c\; 4.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1} \right\rbrack}} \right\}.}} & (8)\end{matrix}$where the interpolating sequences interp20Null, interp40Null,interp80ExtraL, interp80ExtraR and the rotation pattern [c1 c2 c3 c4]are given in FIG. 8 for various non-oversampling and oversampling cases.

In another aspect of the present disclosure, the 80 MHz LTF sequence maybe constructed by using all 20 MHz 802.11a and 40 MHz 802.11n tones.Thus, in any 20 MHz subband, every tone that may be present in 20 MHz802.11a or in 40 MHz 802.11n may have the value of corresponding tonefrom the 20 MHz LTF sequence or the 40 MHz HT-LTF sequence. In addition,the complementary phase rotation sequence may be applied per 20 MHz802.11a bandwidth (i.e., 802.11a tones may be rotated), and a fewmissing tones may be filled.

The constructed 80 MHz LTF sequence may be given as:

$\begin{matrix}{{VHTLTF}_{{- 122},122} = {\left\{ {{c\; 1.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 1.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1} \right\rbrack},{- 1},{- 1},{- 1},1,{{interp}\; 40\;{Null}},{- 1},1,1,{- 1},{c\; 2.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 2.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1} \right\rbrack},{{interp}\; 80\;{ExtraL}},0,0,0,0,0,{{interp}\; 80\;{ExtraR}},{c\; 3.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 3.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1} \right\rbrack},{- 1},{- 1},{- 1},1,{{interp}\; 40\;{Null}},{- 1},1,1,{- 1},{c\; 4.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 4.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1,} \right\rbrack}} \right\}.}} & (9)\end{matrix}$

It can be observed from equation (9) that there may be five subcarriersaround the DC tone, interpolating sequences interp40Null,interp80ExtraL, interp80ExtraR may comprise extra tones to be chosen inan effort to minimize (or at least reduce) the PAPR, and [c1 c2 c3 c4]may represent the complementary sequence. The advantage of this schemeis that there may be no need to store different values for existing 20MHz 802.11a and 40 MHz 802.11n tones. On the other hand, the level ofPAPR may be slightly higher because of less extra tones to be chosen toreduce the PAPR.

FIGS. 9A-9B illustrate an example of PAPR results for 80 MHz LTFsdesigned based on the approach defined by equation (9) in accordancewith certain aspects of the present disclosure. The newly generated LTFsequence given by equation (9) may represent a subset of the previouslygenerated LTF sequence defined by equation (7). Therefore, achieved PAPRresults may not be better than those illustrated in FIGS. 7A-7B.

The preferred 80 MHz LTF sequence constructed based on all 20 MHz802.11a and 40 MHz 802.11n tones and on phase rotation of 20 MHz 802.11asubbands may be given as:

$\begin{matrix}{{VHTLTF}_{{- 122},122} = {\left\{ {{c\; 1.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 1.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1} \right\rbrack},{- 1},{- 1},{- 1},1,{{interp}\; 40\;{Null}},{- 1},1,1,{- 1},{c\; 2.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 2.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1} \right\rbrack},{{interp}\; 80\;{ExtraL}},0,0,0,0,0,{{interp}\; 80\;{ExtraR}},{c\; 3.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 3.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1} \right\rbrack},{- 1},{- 1},{- 1},1,{{interp}\; 40\;{Null}},{- 1},1,1,{- 1},{c\; 4.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 4.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1,} \right\rbrack}} \right\}.}} & (10)\end{matrix}$where the interpolating sequences interp40Null, interp80ExtraL,interp80ExtraR and the rotation pattern [c1 c2 c3 c4] from equation (10)are defined in FIG. 10 for various non-oversampling and oversamplingcases.

In yet another aspect of the present disclosure, the 80 MHz LTF sequencemay be constructed by slightly modifying the constructed LTF sequencedefined by equation (9). All 20 MHz 802.11a and 40 MHz 802.11n tones maybe utilized along with the complementary sequence phase rotation appliedon each 20 MHz bandwidth (i.e., 20 MHz 802.11a tones plus extra datatones of 40 MHz 802.11n). Also, a few missing tones may be filled.Therefore, the constructed 80 MHz LTF sequence may be given as:

$\begin{matrix}{{VHTLTF}_{{- 122},122} = {\left\{ {{c\; 1.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 1.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1} \right\rbrack},{c\; 1.*\left\lbrack {{- 1},{- 1},{- 1},1} \right\rbrack},{{interp}\; 4\; 0\;{Null}},{c\; 2.*\left\lbrack {{- 1},1,1,{- 1}} \right\rbrack},{c\; 2.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 2.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1} \right\rbrack},{{interp}\; 80\;{ExtraL}},0,0,0,0,0,{{interp}\; 80\;{ExtraR}},{c\; 3.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 3*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1} \right\rbrack},{c\; 3.*\left\lbrack {{- 1},{- 1},{- 1},1} \right\rbrack},{{interp}\; 4\; 0\;{Null}},{c\; 4.*\left\lbrack {{- 1},1,1,{- 1}} \right\rbrack},{c\; 4.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},\;{c\; 4.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1} \right\rbrack}} \right\}.}} & (11)\end{matrix}$

It can be observed from equation (11) that there may be five subcarriersaround the DC tone, interpolating sequences interp40Null,interp80ExtraL, interp80ExtraR may comprise extra tones to be chosen inan effort to minimize (or at least reduce) the PAPR, and [c1 c2 c3 c4]may represent the complementary sequence. The newly generated sequencedefined by equation (11) may be different in rotation tone coverage fromthe LTF sequences defined by equations (7) and (9). The advantage ofthis particular scheme is that there may be no need to store differentvalues for existing 20 MHz 802.11a and 40 MHz 802.11n tones. On theother hand, the PAPR may be slightly worse because of less extra tonesto be optimized in an effort to minimize (or at least reduce) the PAPR.

FIGS. 11A-11B illustrate an example of PAPR results for 80 MHz LTFsdesigned based on the approach given by equation (11) in accordance withcertain aspects of the present disclosure. The best PAPR result for thecase of “No rotation 80 Msps” (i.e., 256-point IFFT) is 3.3233 dB, whichis even better than that of the LTF sequence defined by equation (7)(i.e., the PAPR of 3.4239 dB from FIG. 8) due to different rotation tonecoverage.

The preferred 80 MHz LTF sequence constructed based on all 20 MHz802.11a and 40 MHz 802.11n tones and on phase rotation of 20 MHzsubbands may be given as:

$\begin{matrix}{{VHTLTF}_{{- 122},122} = {\left\{ {{c\; 1.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 1.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1} \right\rbrack},{c\; 1.*\left\lbrack {{- 1},{- 1},{- 1},1} \right\rbrack},{{interp}\; 4\; 0\;{Null}},{c\; 2.*\left\lbrack {{- 1},1,1,{- 1}} \right\rbrack},{c\; 2.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 2.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1} \right\rbrack},{{interp}\; 80\;{ExtraL}},0,0,0,0,0,{{interp}\; 80\;{ExtraR}},{c\; 3.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},{c\; 3*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1} \right\rbrack},{c\; 3.*\left\lbrack {{- 1},{- 1},{- 1},1} \right\rbrack},{{interp}\; 4\; 0\;{Null}},{c\; 4.*\left\lbrack {{- 1},1,1,{- 1}} \right\rbrack},{c\; 4.*\left\lbrack {1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1,1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,1,1,1,1} \right\rbrack},\;{c\; 4.*\left\lbrack {1,{- 1},{- 1},1,1,{- 1},1,{- 1},1,{- 1},{- 1},{- 1},{- 1},{- 1},1,1,{- 1},{- 1},1,{- 1},1,1,1,1} \right\rbrack}} \right\}.}} & (12)\end{matrix}$where the interpolating sequences interp40Null, interp80ExtraL,interp80ExtraR and the rotation pattern [c1 c2 c3 c4] from equation (12)are defined in FIG. 12 for various non-oversampling and oversamplingcases.

The proposed approach for designing LTF sequences may be also utilizedfor other numbers of subcarrier tones. For example, in the case of IEEE802.11ac specification, a few tones may be zeroed out at the band edges.Alternatively, all tones around the DC tone may be utilized.

The various operations of methods described above may be performed byany suitable means capable of performing the corresponding functions.The means may include various hardware and/or software component(s)and/or module(s), including, but not limited to a circuit, anapplication specific integrate circuit (ASIC), or processor. Generally,where there are operations illustrated in Figures, those operations mayhave corresponding counterpart means-plus-function components withsimilar numbering. For example, blocks 402-404 and 1302-1306 illustratedin FIG. 4 and FIG. 13 correspond to circuit blocks 402A-404A and1302A-1306A illustrated in FIG. 4A and FIG. 13A.

As used herein, the term “determining” encompasses a wide variety ofactions. For example, “determining” may include calculating, computing,processing, deriving, investigating, looking up (e.g., looking up in atable, a database or another data structure), ascertaining and the like.Also, “determining” may include receiving (e.g., receiving information),accessing (e.g., accessing data in a memory) and the like. Also,“determining” may include resolving, selecting, choosing, establishingand the like.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: a, b, or c” is intended to cover: a, b, c,a-b, a-c, b-c, and a-b-c.

The various operations of methods described above may be performed byany suitable means capable of performing the operations, such as varioushardware and/or software component(s), circuits, and/or module(s).Generally, any operations illustrated in the Figures may be performed bycorresponding functional means capable of performing the operations.

The various illustrative logical blocks, modules and circuits describedin connection with the present disclosure may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array signal (FPGA) or other programmable logic device(PLD), discrete gate or transistor logic, discrete hardware componentsor any combination thereof designed to perform the functions describedherein. A general purpose processor may be a microprocessor, but in thealternative, the processor may be any commercially available processor,controller, microcontroller or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thepresent disclosure may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination of the two. Asoftware module may reside in any form of storage medium that is knownin the art. Some examples of storage media that may be used includerandom access memory (RAM), read only memory (ROM), flash memory, EPROMmemory, EEPROM memory, registers, a hard disk, a removable disk, aCD-ROM and so forth. A software module may comprise a singleinstruction, or many instructions, and may be distributed over severaldifferent code segments, among different programs, and across multiplestorage media. A storage medium may be coupled to a processor such thatthe processor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor.

The methods disclosed herein comprise one or more steps or actions forachieving the described method. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isspecified, the order and/or use of specific steps and/or actions may bemodified without departing from the scope of the claims.

The functions described may be implemented in hardware, software,firmware or any combination thereof. If implemented in software, thefunctions may be stored as one or more instructions on acomputer-readable medium. A storage media may be any available mediathat can be accessed by a computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to carryor store desired program code in the form of instructions or datastructures and that can be accessed by a computer. Disk and disc, asused herein, include compact disc (CD), laser disc, optical disc,digital versatile disc (DVD), floppy disk, and Blu-ray® disc where disksusually reproduce data magnetically, while discs reproduce dataoptically with lasers.

Thus, certain aspects may comprise a computer program product forperforming the operations presented herein. For example, such a computerprogram product may comprise a computer readable medium havinginstructions stored (and/or encoded) thereon, the instructions beingexecutable by one or more processors to perform the operations describedherein. For certain aspects, the computer program product may includepackaging material.

Software or instructions may also be transmitted over a transmissionmedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition oftransmission medium.

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein can bedownloaded and/or otherwise obtained by a user terminal and/or basestation as applicable. For example, such a device can be coupled to aserver to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via storage means (e.g., RAM, ROM, a physical storage mediumsuch as a compact disc (CD) or floppy disk, etc.), such that a userterminal and/or base station can obtain the various methods uponcoupling or providing the storage means to the device. Moreover, anyother suitable technique for providing the methods and techniquesdescribed herein to a device can be utilized.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes and variations may be made in the arrangement, operation anddetails of the methods and apparatus described above without departingfrom the scope of the claims.

While the foregoing is directed to embodiments of the presentdisclosure, other and further embodiments of the disclosure may bedevised without departing from the basic scope thereof, and the scopethereof is determined by the claims that follow.

The invention claimed is:
 1. A method for wireless communications,comprising: constructing a long training field (LTF) sequence for afirst bandwidth by combining a plurality of interpolating sequences andone or more other sequences repeated multiple times; applying phaserotation to at least one of a plurality of portions of the firstbandwidth, each portion including a plurality of symbols; andtransmitting the constructed LTF sequence over a wireless channel byutilizing a bandwidth of the first size.
 2. The method of claim 1,wherein constructing the LTF sequence comprises: designing the pluralityof interpolating sequences in an effort to reduce the PAPR.
 3. Themethod of claim 1, further comprising: performing oversampling prior tothe transmission.
 4. The method of claim 1, wherein the bandwidth of thefirst size comprises a bandwidth of 80 MHz.
 5. An apparatus for wirelesscommunications, comprising: a constructing circuit configured toconstruct a long training field (LTF) sequence by combining a pluralityof interpolating sequences and one or more other sequences repeatedmultiple times, and applying phase rotation to at least one of aplurality of portions of the first bandwidth, each portion including aplurality of symbols; and a transmitter configured to transmit theconstructed LTF sequence over a wireless channel by utilizing abandwidth of a first size.
 6. The apparatus of claim 5, wherein theconstructing circuit is also configured to design the plurality ofinterpolating sequences in an effort to reduce the PAPR.
 7. Theapparatus of claim 5, further comprising: a sampler configured toperform oversampling prior to the transmission.
 8. The apparatus ofclaim 5, wherein the bandwidth of the first size comprises a bandwidthof 80 MHz.
 9. An apparatus for wireless communications, comprising:means for constructing a long training field (LTF) sequence by combininga plurality of interpolating sequences and one or more other sequencesrepeated multiple times; means for applying phase rotation to at leastone of a plurality of portions of the first bandwidth, each portionincluding a plurality of symbols; and means for transmitting theconstructed LTF sequence over a wireless channel by utilizing abandwidth of a first size.
 10. The apparatus of claim 9, wherein themeans for constructing the LTF sequence comprises: means for designingthe plurality of interpolating sequences in an effort to reduce thePAPR.
 11. The apparatus of claim 9, further comprising: means forperforming oversampling prior to the transmission.
 12. The apparatus ofclaim 9, wherein the bandwidth of the first size comprises a bandwidthof 80 MHz.
 13. A computer-program product for wireless communications,comprising a non-transitory computer-readable medium comprisinginstructions executable to: construct a long training field (LTF)sequence by combining a plurality of interpolating sequences and one ormore other sequences repeated multiple times; apply a phase rotation toat least one of a plurality of portions of the first bandwidth, eachportion including a plurality of symbols; and transmit the constructedLTF sequence over a wireless channel by utilizing a bandwidth of a firstsize.
 14. A method for wireless communications, comprising: constructinga long training field (LTF) sequence by combining a plurality ofinterpolating sequences with LTF symbol values associated with at leastone of the IEEE 802.11n standard or the IEEE 802.11a standard, whereinthe LTF symbol values cover at least a portion of bandwidth of a firstsize, and each of the LTF symbol values is repeated one or more timesfor different subcarriers; rotating phases of symbols of the LTFsequence per bandwidth of the first size; and transmitting the LTFsequence over a wireless channel by utilizing a bandwidth of a secondsize.
 15. The method of claim 14, wherein the bandwidth of the firstsize comprises a bandwidth of 20 MHz.
 16. The method of claim 14,wherein the bandwidth of the first size comprises a bandwidth of 40 MHz.17. The method of claim 14, wherein the bandwidth of the second sizecomprises a bandwidth of 80 MHz.